Clothing made from cellulosic fabrics such as cotton and in particular indigo dyed denim have been common for many years. Recently, consumers have preferred the denim to look preworn and feel softer. This preworn look and softer feel can be accomplished by fabric finishing processes such as prewashing or stonewashing where the fabric is treated to release dye from the fabric. In this invention, we define a "fabric finishing process" as any process which includes one or more steps where dye is released from fabric or clothing.
The most common dye used to dye denim is indigo blue which is classified as a vat dye. Indigo blue is the most common dye that is released in a stonewashing or prewashing process. Other dyes, such as sulfur black are also used to color denim and could also be released in a fabric finishing process.
Prewashing the fabric can accomplish one or more of the following effects: 1) uniform fading of the fabric by bleeding excess dye, 2) softening the fabric by removing sizing, a stiffening agent used to facilitate cutting the fabric, 3) preshrinking the fabric, and 4) improving the hand of the fabric.
A typical fabric prewashing process, for example, may begin with a 15 to 20 minute wash cycle using a conventional alkaline laundry detergent formula, followed by a souring rinse to remove alkalinity developed by the detergent, a fresh water rinse, a fabric softening rinse, and a water extraction cycle. A typical laundry detergent may contain, for example, nonionic and ionic surfactants, builders, soil anti-redeposition agents, optical brighteners, and fillers. Several variations in this prewashing process have been made. For example, U.S. Pat. No. 4,388,077 describes the use of an amphoteric surfactant and builder in a detergent composition to improve preshrinking, dye-bleeding, and fabrics softening results. Alternatively, U.S. Pat. No. 4,218,220 adds an additional bleaching step after the wash cycle. Specifically, this additional step consists of contacting the fabric or clothing with an aqueous solution containing bleach and fabric softener to produce a more uniform fade. In the present invention, we define the term "prewashing" to include those processes which uniformly fade the fabric.
Stonewashing the fabric or clothing accomplishes the following effects: 1) non uniformly fades the fabric such that the color density in the fabric varies throughout the fabric, 2) softens the fabric, 3) makes the fabric surface appear fuzzy. The stonewashing process in contrast to the prewashing process produces a more preworn look.
The stonewashing process traditionally involves contacting wetted denim clothing in large tub equipment with pumice stones having a particle size of about 1 to 10 inches and with smaller pumice particles generated by the abrasive nature of the process. The pumice abrades the fabric producing in the denim localized areas of lighter color and similar lightened areas in the seams. Additionally, the pumice softens the fabric and produces a fuzzy surface similar to that produced by extended wear of the fabric. One or more chemicals may be included with the pumice stones, such as for example surfactant, bleach, and builders. Additionally, other abrasive materials can be used instead of the pumice such as ceramic balls used in ball mills, and irregular hard rubber pieces. After the washing step, the fabric or clothing is typically rinsed one or more times in an aqueous solution. The aqueous solution may include such additives as fabric softeners, or neutralizing agents.
As with the prewashing process, variations of the stonewashing process have been reported. U.S. Pat. No. 4,740,213 discloses a dry method for stonewashing where pumice, impregnated with a chemical bleaching agent, is brought into contact with the fabric to produce a more random faded look. Following dry contact of the fabric or clothes with the pumice stones, the fabric is rinsed with an aqueous solution to neutralize the bleach. Another variation to the stonewashing process is disclosed in U.S. Pat. No. 4,832,864 where a detergent composition containing cellulase enzymes is used instead of an abrasive like pumice to degrade and non uniformly fade the fabric. Also, cellulase enzymes may be used in combination with pumice stones and optionally other chemicals such as surfactants, builders, buffering agents to produce a preworn look and feel. In the present invention, we define "stonewashing" as a process that produces a nonuniform fading of the fabric.
Unfortunately, during fabric finishing processes, these released dyes can deposit back onto the denim and white pocket liners. Because of this deposition, the pocket liners become undesirably colored and the denim has a darker appearance on the seams of the clothing. Fabrics may-also appear "blotchy" meaning that certain locations on the fabric may appear darker or lighter than other locations on the same fabric. Neither colored pocket liners, nor darkened seams and threads, nor blotchy fabric are acceptable. DE 3124210 A-1 discloses a liquid detergent composition containing a surfactant and a polymer that is effective for preventing dye transfer during laundry operations. However, DE 3124210 A-1 does not address the problem of preventing dye deposition in a fabric finishing process specifically designed to release dye from the fabric. The problem of dye deposition in stonewashing and prewashing is more severe because the concentration of dye in the wash bath is at least 100 percent higher than in a typical household laundry process. Consequently, a fabric finishing process and dye deposition inhibiting agents are needed that will be effective in preventing dye from depositing on fabric under these stressed conditions.
Accordingly, one aspect of this invention is to provide fabric finishing compositions containing one or more dye deposition inhibiting agents which can be added during fabric finishing processes to effectively inhibit the deposition of dye during these processes.
A further aspect of this invention is to provide a process to inhibit the deposition of released dyes during prewashing or stonewashing.